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Related Party Transactions (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Related Party Transaction [Line Items]
Services and other revenues	$ 617,638	$ 565,861
Reinsurance recoverables	9,575,066		$ 9,235,501
Premiums ceded	1,708,362	1,218,234
Nephila Reinsurers [Member]
Related Party Transaction [Line Items]
Reinsurance recoverables	785,900		794,300
Hagerty, Inc. [Member]
Related Party Transaction [Line Items]
Reinsurance recoverables	225,300		$ 214,800
Gross premium volume	198,282	164,971
Premiums ceded	152,685	124,628
Insurance-linked Securities Operations [Member] | Unconsolidated entities managed by Nephila [Member]
Related Party Transaction [Line Items]
Services and other revenues	19,200	9,800
Program services and other fronting [Member] | Nephila Reinsurers [Member]
Related Party Transaction [Line Items]
Gross premium volume	353,100	236,900
Premiums ceded	$ 353,100	$ 236,900

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Amount, after valuation allowance, recoverable under reinsurance contracts. Examples include, but are not limited to, settled and unsettled claims, incurred but not reported losses, loss adjustment expense, policy benefits and policy reserves. Excludes premiums paid under reinsurance contracts.

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